The present invention is directed to orthodontic brackets and, particularly, to brackets having improved characteristics and made of ceramic materials.
The brackets which are used in orthodontic work, and specifically attached to a tooth and joined to other teeth via wires which interconnect with the brackets, are basic to orthodontic dentistry. These brackets have severe and sometimes conflicting service requirements. It is preferable that they have satisfactory asthetic appearance which generally requires white or off-white color. They must have sufficiently high mechanical properties to withstand the severe mechanical stresses placed upon them in use. They must have sufficient abrasion resistance so that they are not unduly abraded by the wires or by contact with food during chewing. They must also be resistant to the fluids in the oral cavity, which resistance would best be achieved by having a bracket which is nonporous or of minimal porosity. It is also necessary that the bracket have suitable characteristics so that it may be adhered to the tooth. Since good adhesion often involves providing a porous bonding surface, this surface requirement is sometimes in conflict with the desirability of the bracket to otherwise have minimal porosity.
Traditionally, brackets have been formed from metals. Metals suffer the disadvantage of their unsightly appearance on teeth. Attempts have been made to overcome this disadvantage by coating the metal, e.g., as disclosed in U.S. Pat. No. 4,050,156. Coating techniques suffer a number of disadvantages, including the tendency for coatings to chip or flake off if they are sufficiently hard to have good abrasion resistance and the tendency for coatings which have good adhesion to be poor in abrasion resistance. Plastic brackets have also been utilized. While plastic brackets have a satisfactory asthetic appearance, they generally have the disadvantage of poor mechanical properties and some difficulties in manufacture.
The object of the present invention is to provide for improved orthodontic brackets having satisfactory asthetic appearance, satisfactory mechanical properties and which are suitable for practical manufacture from ceramic materials.